The present invention relates to an intake manifold of an internal combustion engine for use with, for example, an automobile, which manifold is suitable for lowering the temperature of air to be sucked into the engine.
Various methods have been employed in the past to increase the outputs of automotive internal combustion engines. The methods include supercharging which is to raise the pressure of intake air to positively increase the quantity of air fed into an internal combustion engine. Another method is to improve the shape of the engine intake manifold so that the inertia of intake air or the effect of pulsation of the intake air is utilized to increase the quantity of air fed into the engine. A still further method is termed an "intercooler method" by which, as disclosed in a Japanese Magazine, "Jidosha Kogaku (Automotive Engineering)", Vol. 35, No. 7, pages 106-108, the engine intake manifold is disposed adjacent to the front grille of the car to expose the intake manifold to outdoor air so as to remove heat from the intake air for thereby increasing the quantity of air fed into the engine.
While the prior art methods are all effective to increase the quantities of air to be supplied into internal combustion engines, the temperature of engine intake air has not been taken into consideration in the prior art. It will be appreciated that the intercooling method cannot lower the temperature of intake air below the outdoor air temperature. If the intake air temperature is high, the compression stroke in the engine cylinder commences at a correspondingly high temperature which tends to cause an abnormal combustion, with a disadvantageous result in that, even if the quantity of intake air is greatly increased, the compression ratio cannot be increased too much.